A spectral apparatus including a polychromator, includes sensors that output signals indicating the respective energy amounts of a plurality of wavelength components. Spectral characteristics, such as spectral reflectance, spectral radiance, and spectral transmittance, are acquired from the plurality of signals output by the plurality of sensors.
The spectral sensitivity of each of the sensors varies depending on, for example, the arrangement, shape, and size of a light-receiving sensor, and varies depending on, for example, the arrangement, shape, and size of a slit plate or a diffraction grating included in the polychromator. Therefore, the spectral sensitivity of such a sensor, fundamental in the spectral characteristics, must be calibrated per spectral apparatus.
A wavelength calibration method of a spectral apparatus described in Patent Literature 1, includes: giving a difference from the reference value of the center wavelength in spectral sensitivity by a linear function of pixel number (paragraph 0026); giving a ratio to the reference value of the full width at half maximum in the spectral sensitivity by a linear function of pixel number (paragraph 0028); creating a corrected spectral sensitivity table with the difference from the reference value of the center wavelength in the spectral sensitivity and the ratio to the reference value of the full width at half maximum in the spectral sensitivity (paragraph 0029), and determining coefficients included in each of the linear functions of pixel number such that calculated relative output calculated with the corrected spectral sensitivity table and emission-line wavelengths and measured relative output are values closest to each other (paragraph 0033).